Pneumatic actuators are motion control devices that are used to cause and control motion. Such actuators commonly include a pneumatic chamber to which pneumatic pressure is selectively connected and vented, and a piston head in the chamber that is acted upon and moved by the pneumatic pressure. The movement of the piston head is transferred to an output member that is to be moved.
One type of pneumatic actuator includes a spring that biases the output member to a first or normal or at rest position. When the pneumatic pressure is connected to the pneumatic chamber so that it acts against and moves the piston, this movement of the piston causes the output member to move against the bias of the spring to a second or actuated position.
For certain uses of pneumatic actuators of this type, it is desirable to provide a high spring bias force and a resulting high output force of the output member. This high output force is able to move large loads to a first position and hold those loads in that position for indeterminate lengths of time without pneumatic pressure input. It is also desirable for pneumatic actuators of this type to overcome the bias of the high spring force, and cause and control movement of the output member to a second position, with low, readily available pneumatic pressure (commonly called shop air pressure). Furthermore, it is desirable to provide such a pneumatic actuator that is compact in size for use in confined spaces.
One application for pneumatic actuators of the general type described above is to operate high pressure valves that control the flow of high pressure fluid. In this application, the pneumatic actuator may be secured to a standard mounting arrangement on the high pressure valve, and the output member may control the operation of the valve. The spring biased first position of the output member holds the valve in one position, and movement of the output member to its second position by operation of pneumatic pressure on the piston head allows the valve to move to another position.